Storage control device, storage control method, and recording medium

ABSTRACT

A storage control device according to the present invention connected to a master disk device that stores data into a plurality of segments continuously, and a plurality of copy disk devices that are copy destinations of the data, the storage control device includes: a clone processing unit that, when receiving a copy instruction for one of the copy disk devices, repeats reading and writing of each of the segments in order of address to complete copy, and that, when a first copy disk that is the copy disk device other than a later copy disk that is the specified copy disk device is during copy when receiving the copy instruction, starts copy of the later copy disk from the segment during reading, and, after the completion of reading data of the segment, performs writing into both the first copy disk and the later copy disk.

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2016-042479, filed on Mar. 4, 2016, thedisclosure of which is incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention relates to a storage control device, a storagecontrol method, and a recording medium, in particular, a storage controldevice, a storage control method, and a recording medium, which create aplurality of clone disks of a master disk.

BACKGROUND ART

Japanese Unexamined Patent Application Publication No. 2015-46159discloses a system in which, after one virtual machine that becomes amaster is created, a clone of the master virtual machine is created, anda plurality of new virtual machines are created, when using a pluralityof virtual machines by using a virtual environment.

SUMMARY

The creation of the clone of the master virtual machine is performed bycopying a logical disk that is a component of the virtual machine thatbecomes a master (hereinafter, master disk) into another logical disk,and constructing a new virtual machine by using the copied logical disk(hereinafter, clone disk). When creating a plurality of new virtualmachines simultaneously, processing of creating the respective newvirtual machines is executed a synchronously. Thus, the creation of therespective clone disks is performed separately and a synchronously.

Since data copies from one master disk into a plurality of clone disksare executed a synchronously, reading of all data of the master disk isperformed each time when the clone disk creation is required. Thus,there is a problem in that, the load of the master disk is increased asthe number of requests for the clone disk creation grows, and, as aresult, it takes time to perform reading processing from the masterdisk, and processing time of the clone disk creation is lengthened.

This problem occurs when a plurality of clone disks are created from onemaster disk a synchronously without limitation to when the clone of thevirtual machine is created. The disks may be logical disks or actualdisks (physical disks).

It is an object of the present invention to provide a storage controldevice, a storage control method, and a recording medium, which solvethe above-described problem.

A storage control device according one aspect of the present inventionis connected to a master disk device that stores data into a pluralityof segments continuously, and a plurality of copy disk devices that arecopy destinations of the data. The storage control device includes: aclone processing unit that, when receiving a copy instruction for one ofthe copy disk devices, repeats reading and writing of each of thesegments in order of address to complete copy, and that, when a firstcopy disk that is the copy disk device other than a later copy disk thatis the specified copy disk device is during copy when receiving the copyinstruction, starts copy of the later copy disk from the segment duringreading, and, after the completion of reading data of the segment,performs writing into both the first copy disk and the later copy disk.

A storage control method according to one aspect of the presentinvention is a method of a storage control device. The storage controldevice is connected to a master disk device that stores data into aplurality of segments continuously, and a plurality of copy disk devicesthat are copy destinations of the data. The storage control method isperformed by the storage control device. The storage control methodincludes: receiving a copy instruction for one of the copy disk devices,and repeating reading and writing of each of the segments in order ofaddress to complete copy; and when a first copy disk that is the copydisk device other than a later copy disk that is the specified copy diskdevice is during copy when receiving the copy instruction, starting copyof the later copy disk from the segment during reading, and, after thecompletion of reading data of the segment, performing writing into boththe first copy disk and the later copy disk.

A computer readable non-transitory recording medium according to oneaspect of the present invention embodies a program. The program causes acomputer to perform a method. The computer is connected to a master diskdevice that stores data into a plurality of segments continuously, and aplurality of copy disk devices that are copy destinations of the data.The method includes: receiving a copy instruction for one of the copydisk devices, and repeating reading and writing of each of the segmentsin order of address to complete copy, and, when a first copy disk thatis the copy disk device other than a later copy disk that is thespecified copy disk device is during copy when receiving the copyinstruction, starting copy of the later copy disk from the segmentduring reading, and, after the completion of reading data of thesegment, performing writing into both the first copy disk and the latercopy disk.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary features and advantages of the present invention will becomeapparent from the following detailed description when taken with theaccompanying drawings in which:

FIG. 1 is a configuration diagram of a storage system 40 according to afirst example embodiment;

FIG. 2 is a configuration diagram of a computer device 50;

FIG. 3 is a configuration diagram of data stored in a management table11;

FIG. 4 is an operation flow chart of a clone processing unit 12;

FIG. 5 is a diagram illustrating a process of executing copy withrespect to three clone disk devices 21 (illustrated by clone disks 1, 2,and 3, respectively) (part 1);

FIG. 6 is a diagram illustrating the process of executing copy withrespect to the three clone disk devices 21 (illustrated by clone disks1, 2, and 3, respectively) (part 2);

FIG. 7 is a diagram illustrating the process of executing copy withrespect to the three clone disk devices 21 (illustrated by clone disks1, 2, and 3, respectively) (part 3);

FIG. 8 is a diagram illustrating the process of executing copy withrespect to the three clone disk devices 21 (illustrated by clone disks1, 2, and 3, respectively) (part 4);

FIG. 9 is a diagram illustrating the process of executing copy withrespect to the three clone disk devices 21 (illustrated by clone disks1, 2, and 3, respectively) (part 5); and

FIG. 10 is a configuration diagram of a storage control device 10according to a second example embodiment.

EXEMPLARY EMBODIMENT First Example Embodiment

<Outline>

A storage control device 10 according to the present example embodimentreceives a plurality of data-copy-requests transmitted from a masterdisk device 20 into clone disk devices 21 a synchronously andcontinuously in a short period of time. When receiving thedata-copy-request into each of the clone disk devices 21, the storagecontrol device 10 stores an address where copying data into the clonedisk device 21 specified by the data-copy-request is started(hereinafter, copy start address) in association with the clone diskdevice 21.

The storage control device 10 performs reading from the master diskdevice 20 sequentially, and performs writing into each of the clone diskdevices 21 sequentially with the copy start address stored inassociation with the clone disk device 21 as a starting point.

Accordingly, the storage control device 10 reduces the data readingvolume with respect to the master disk device 20, and shortens the datacopy time into the clone disk devices 21.

<Configuration>

FIG. 1 is a configuration diagram of a storage system 40 according to afirst example embodiment. The storage system 40 includes the storagecontrol device 10, the master disk device 20 connected to the device,the plurality of the clone disk devices 21, and a management serverdevice 30.

The master disk device 20 and the clone disk devices 21 have similar incapacity. The master disk device 20 and the clone disk devices 21 may bephysical disk devices, respectively, or logical disk devices provided inone physical disk device. In addition, three clone disk devices 21 areillustrated in FIG. 1, but the number of the clone disk devices 21 isnot limited to three.

The master disk device 20 stores original data to be copied into theclone disk devices 21. The original data is composed of a plurality ofpieces of segment data, for example, a plurality of blocks, and asegment ID (Identifier) is allocated to each of them. The segment ID is,for example, a segment sequence number, a segment initial address, or asegment final address.

The original data stored in the master disk device 20 is illustrated inthe upper stage of FIG. 5. In the example of FIG. 5, the original datais composed of three segments denoted by (1), (2), and (3). The numberof the segments is not limited to three.

In the present example embodiment, the segments are managed circularly.Here, the term circularly means that, for example, the segment (1) isfollowed by the segment (2) and then by the segment (3) to return to thesegment (1).

In other words, the term circularly means that reading and writing ofthe segments are operated continuously in order of address such that thesegment having the lowest address is targeted after the segment havingthe highest address.

The storage control device 10 includes a clone processing unit 12 and amanagement table 11.

The clone processing unit 12 receives a data-copy-request that targetsany one of the clone disk devices 21 from the management server device30, and executes copying data from the master disk device 20 into thespecified clone disk device 21. The clone processing unit 12 can receivea plurality of data-copy-requests targeting the clone disk device 21sequentially to execute copy thereof concurrently. The clone processingunit 12 controls the master disk device 20 such that reading data fromthe master disk device 20 is performed sequentially when executing thedata copy.

As just described, the management server device 30 is one example of amanagement device.

The clone processing unit 12 is configured by a logic circuit. The cloneprocessing unit 12 may be achieved by a program 53 that the storagecontrol device 10 that is also a computer device 50 executes.

FIG. 2 is a configuration diagram of the computer device 50. Thecomputer device 50 includes a processor 51 and a main storage unit 52which are connected to each other with a bus 55. Here, the main storageunit 52 is, for example, a semiconductor storage device. The mainstorage unit 52 stores the program 53.

The semiconductor storage device is, for example, a flash Read OnlyMemory (ROM), a Solid State Drive (SSD), or a Random Access Memory(RAM). That is, the main storage unit 52 is a computer-readablenon-transitory recording medium and/or transitory recording medium.

The program 53 is executed by the processor 51 to make the processor 51function as the clone processing unit 12.

FIG. 3 is a configuration diagram of data stored in the management table11. The management table 11 stores a read segment ID variable, a writesegment ID variable, and copy start segment ID variables and statevariables which are provided in association with the respective clonedisk devices 21.

The read segment ID variable stores a segment ID of a segment duringreading, during reading data from the master disk device 20 in a copyprogressing process. The read segment ID variable is advanced (added)when reading of the segment data is completed.

The write segment ID variable stores a segment ID of a segment duringwriting, during writing data into the clone disk device 21 in the copyprogressing process. The write segment ID variable is advanced (added)when writing of the segment data is completed. In both the read segmentID variable and the write segment ID variable, an initial value is, forexample, the segment ID of the initial segment of the original data.

The state variable indicates a state in a copy process of the associatedclone disk device 21. There are three types of states: not targeted(initial value); waiting for processing; and during processing.

The copy start segment ID variable stores a segment ID of a segmentwhere copy of the associated clone disk device 21 is started.

The management table 11 is stored in a storage region of the storagecontrol device 10. The management table 11 is stored in, for example,the main storage unit 52 of the computer device 50.

<Operation>

FIG. 4 is an operation flow chart of the clone processing unit 12. Theclone processing unit 12 is activated when receiving a data copyinstruction from the management server device 30.

In other words, the management server device 30 (management device)transmits the copy instruction to the storage control device 10.

In the following description, the read segment ID is a value of the readsegment ID variable, and other segment IDs follow this example.

When being activated, the clone processing unit 12 stores the readsegment ID in the copy start segment ID variable associated with theclone disk device 21 specified by the copy request (S21). Then, duringnon-writing in the data copy process (N in S22), the clone processingunit 12 records “during processing” in the state variable associatedwith the clone disk device 21 (S23). Finally, in the case of no longerduring reading of the master disk device 20, more specifically, in thecase of not during reading for copy of another clone disk device 21, theclone processing unit 12 issues a reading instruction of the segmentindicated by the read segment ID to the master disk device 20 (S24).

During writing in the data copy process (Y in S22), the clone processingunit 12 records “waiting for processing” in the state variableassociated with the clone disk device 21 specified by the copy request(S31). This is because, when writing is already performed, copy of theclone disk device 21 is waited until copy of the next segment is started(S3, S4).

The clone processing unit 12 is activated also when reading of themaster disk device 20 is completed, and advances the read segment ID tothe next segment ID (S11). This advance is performed circularly, asdescribed above.

Then, for segments of write segment IDs of all of the clone disk devices21 associated with state variables indicating “during processing”, theclone processing unit 12 starts writing of data for which reading iscompleted (S12).

The clone processing unit 12 is activated also when writing to all ofthe clone disk devices 21, which is started in S12, is completed, andadvances the write segment ID to the next segment ID (S1). This advanceis performed circularly, as described above.

Next, among the clone disk devices 21 in which the state variable valueis “during processing”, the clone processing unit 12 gives notice ofcompletion for those in which copy is completed (S2). The cloneprocessing unit 12 determines whether copy is completed, for example,determines that copy is completed with respect to a clone disk device 21in which the copy start segment ID corresponds to the read segment ID.For each of the clone disk devices 21, the clone processing unit 12counts the number of the segments in which copy is completed, and maydetermine that copy is completed with respect to a clone disk device 21in which the number of the segments of the original data of the masterdisk device 20 corresponds to the number of the segments in which copyis completed.

When there is a clone disk device 21 in which the state variable valueis “waiting for processing”, the clone processing unit 12 changes thestate variable value to “during processing” (S3). Finally, when there isa clone disk device 21 in which the associated state variable is “duringprocessing”, the clone processing unit 12 starts reading of the segmentof the master disk device 20 indicated by the read segment ID (S4).

At the completion of reading data from the master disk device 20, theclone processing unit 12 may start writing of data of the segment inwhich reading is completed into the clone disk device 21 (S12) and startreading of data of the next segment simultaneously.

FIG. 5 to FIG. 9 are diagrams illustrating a process of executing copywith respect to three clone disk devices 21 (illustrated by clone disks1, 2, and 3, respectively). In this example, the master disk device 20stores data composed of three segments (illustrated by (1), (2), and(3), respectively). In this example, the copy start segment ID isillustrated as a start address of a copy segment, the read segment ID isillustrated as a read address, and the write segment ID is illustratedas a write address. Start addresses of copy start segments of the clonedisks 1, 2, and 3 are illustrated as copy start addresses 1, 2, and 3.

In FIG. 5, when receiving a data-copy-request for the clone disk 1 firstafter starting of operation of the storage system 40, the cloneprocessing unit 12 sets the read address to the copy start address ofthe clone disk 1. Here, the copy start address 1 becomes a start addressof the segment (1). Then, the clone processing unit 12 starts to copydata of the segment (1) of the master disk indicated by the read addressinto the segment (1) of the clone disk 1 indicated by the write address1.

In FIG. 6, when receiving a data-copy-request for the clone disk 2during writing into the segment (1) of the clone disk 1 (double-linedarrow in the drawing), the clone processing unit 12 sets the readaddress to the copy start address of the clone disk 2. Here, the copystart address 2 becomes a start address of the segment (2). After thecompletion of writing into the segment (1) of the clone disk 1, theclone processing unit 12 starts to copy data of the segment (2) of themaster disk indicated by the read address into the segments (2) of theclone disks 1 and 2 indicated by the write addresses. At this time, copyinto the segment (1) of the clone disk 1, which is hatched in thedrawing, is completed.

In FIG. 7, when receiving a data-copy-request for the clone disk 3during writing into the segments (2) of the clone disks 1 and 2(double-lined arrows in the drawing), the clone processing unit 12 setsthe read address to the copy start address of the clone disk 3. Here,the copy start address 3 becomes a start address of the segment (3).After the completion of writing into the segments (2) of the clone disks1 and 2, the clone processing unit 12 starts to copy data of the segment(3) of the master disk indicated by the read address into the segments(3) of the clone disks 1, 2, and 3 indicated by the write addresses. Atthis time, copies into the segment (1) and (2) of the clone disk 1 andthe segment (2) of the clone disk 2, which are hatched in the drawing,are completed.

In FIG. 8, after the completion of writing into the segments (3) of theclone disks 1, 2, and 3 (double-lined arrows in the drawing), the cloneprocessing unit 12 notifies the management server device 30 of copycompletion of the clone disk 1 in which the copy start address 1corresponds to the read address. Then, the clone processing unit 12starts to copy data of the segment (1) of the master disk indicated bythe read address into the segments (1) of the clone disks 2 and 3indicated by the write addresses. At this time, copies into all of thesegments of the clone disk 1, the segments (2) and (3) of the clone disk2, and the segment (3) of the clone disk 3, which are hatched in thedrawing, are completed.

In FIG. 9, after the completion of writing into the segments (1) of theclone disks 2 and 3 (double-lined arrows in the drawing), the cloneprocessing unit 12 notifies the management server device 30 of copycompletion of the clone disk 2 in which the copy start address 2corresponds to the read address. Then, the clone processing unit 12starts to copy data of the segment (2) of the master disk indicated bythe read address into the segment (2) of the clone disk 3 indicated bythe write address. At this time, copies into all of the segments of theclone disks 1 and 2 and the segments (1) and (3) of the clone disk 3,which are hatched in the drawing, are completed.

Then, after the completion of writing into the segment (2) of the clonedisk 3, the clone processing unit 12 notifies the management serverdevice 30 of copy completion of the clone disk 3 in which the copy startaddress 3 corresponds to the read address, and finishes copy of theclone disks 1, 2, and 3.

<Effect>

The storage control device 10 according to the present exampleembodiment can perform copy at high speed even when copying data intothe plurality of clone disk devices 21 from one master disk device 20are executed a synchronously.

The first reason is that, when receiving a data-copy-request into aclone disk device 21, the clone processing unit 12 sets the writesegment ID of the clone disk device 21 so as to perform data readingfrom the master disk device 20 by a sequential reading operation.Accordingly, seek operation of the master disk device 20 is effectivelyperformed.

The second reason is that the clone processing unit 12 can write data,read one time from the master disk device 20, into the plurality ofclone disk devices 21. More specifically, the clone processing unit 12need not read data from the master disk device 20 each time, withrespect to each of the clone disk devices 21 that are targets to becopied.

Accordingly, the storage control device 10 can perform copy at highspeed by reducing the load of data read of the master disk device 20.

Second Example Embodiment

FIG. 10 is a configuration diagram of the storage control device 10according to a second example embodiment.

The storage control device 10 is connected to the master disk device 20that stores data into a plurality of segments continuously, and theplurality of clone disk devices 21 that are copy destinations of thedata.

The storage control device 10 includes the clone processing unit 12that, when receiving a copy instruction for any one of the clone diskdevices 21, repeats reading and writing of each of the segments in orderof address to complete copy. When a first copy disk, that is a copy diskdevice other than a later copy disk that is the specified clone diskdevice 21, is during copy when receiving the copy instruction, the cloneprocessing unit 12 starts copy of the later copy disk device from thesegment during reading, and, after the completion of reading data of thesegment, performs writing into both the first copy disk and the latercopy disk.

The storage control device 10 according to the present exampleembodiment can perform copy at high speed even when copying data intothe plurality of clone disk devices 21 from one master disk device 20are executed a synchronously.

The first reason is that, when receiving a data-copy-request to a clonedisk device 21, the clone processing unit 12 sets the write segment IDof the clone disk device 21 so as to perform data reading from themaster disk device 20 by a sequential reading operation. Accordingly,seek operation of the master disk device 20 is effectively performed.

The second reason is that the clone processing unit 12 can write dataread one time from the master disk device 20 into the plurality of clonedisk devices 21. More specifically, the clone processing unit 12 neednot read data from the master disk device 20 each time, with respect toeach of the clone disk devices 21 that are targets to be copied.

Accordingly, the storage control device 10 can perform copy at highspeed by reducing the load of data read of the master disk device 20.

While the invention has been particularly shown and described withreference to example embodiments thereof, the invention is not limitedto these embodiments. It will be understood by those of ordinary skillin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the claims.

The whole or part of the example embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A storage control device connected to a master disk device that storesdata into a plurality of segments continuously, and a plurality of copydisk devices that are copy destinations of the data, the storage controldevice includes:

a clone processing unit that, when receiving a copy instruction for oneof the copy disk devices, repeats reading and writing of each of thesegments in order of address to complete copy, and

that, when a first copy disk that is the copy disk device other than alater copy disk that is the specified copy disk device is during copywhen receiving the copy instruction, starts copy of the later copy diskfrom the segment during reading, and, after the completion of readingdata of the segment, performs writing into both the first copy disk andthe later copy disk.

(Supplementary Note 2)

The storage control device according to supplementary note 1, wherein

the clone processing unit

(1) continues reading and writing of the segments in order of circularaddress such that the segment having the lowest address is targetedafter the segment having the highest address, as long as there is thecopy disk device during copy, and

(2) gives notice of completion for the copy disk device in which copy ofall of the segments is completed.

(Supplementary Note 3)

The storage control device according to supplementary note 2, furtherincludes:

a storage region in a management table storing a read segment IDvariable that stores a segment ID that is an identifier of the segmentduring reading, a write segment ID variable that stores the segment IDduring writing, and a copy start segment ID variable that stores thesegment ID where copy is started with respect to each of the copy diskdevices during copy, during reading the master disk device, wherein

the clone processing unit

(1) stores, when receiving the copy instruction during reading themaster disk device, a value of the read segment ID variable in the copystart segment ID variable of the copy disk device specified by the copyinstruction,

(2) when reading of the master disk device is completed,

-   -   (a) advances the value of the read segment ID variable to the        next segment ID in order of the circular address,    -   (b) starts writing of the read data into the segments indicated        by the write segment ID variable of all of the copy disk devices        during copy,

(3) when writing of all of the copy disk devices is completed,

-   -   (a) advances a value of the write segment ID variable to the        next segment ID in order of the circular address,    -   (b) among the copy disk devices during copy, determines those in        which copy of all segments is completed on the basis of the copy        start segment ID variable, and gives notice of completion, and,    -   (c) when there is the copy disk device during copy, starts        reading from the segment indicated by the read segment ID        variable of the master disk device.

(Supplementary Note 4)

The storage control device according to any one on supplementary notes 1to 3, wherein

-   -   each of the segment IDs is a start address of the segments or a        sequence number.

(Supplementary Note 5)

A storage system including:

the storage control device of any one of supplementary notes 1 to 4;

a management device that transmits the copy instruction to the storagecontrol device and receives the notice of completion;

the master disk device; and

the plurality of copy disk devices.

(Supplementary Note 6)

A storage control method of a storage control device connected to amaster disk device that stores data into a plurality of segmentscontinuously, and a plurality of copy disk devices that are copydestinations of the data, the storage control method includes:

by the storage control device,

receiving a copy instruction for one of the copy disk devices, andrepeating reading and writing of each of the segments in order ofaddress to complete copy; and

when a first copy disk that is the copy disk device other than a latercopy disk that is the specified copy disk device is during copy whenreceiving the copy instruction, starting copy of the later copy diskfrom the segment during reading, and, after the completion of readingdata of the segment, performing writing into both the first copy diskand the later copy disk.

(Supplementary Note 7)

The storage control method according to supplementary note 6, furtherincludes:

by the storage control device,

(1) continuing reading and writing of the segments in order of circularaddress such that the segment having the lowest address is targetedafter the segment having the highest address, as long as there is thecopy disk device during copy, and

(2) giving notice of completion for the copy disk device in which copyof all of the segments is completed.

(Supplementary Note 8)

The storage control method according to supplementary note 7, furtherincludes:

with the use of a storage region in a management table storing a readsegment ID variable that stores a segment ID that is an identifier ofthe segment during reading, a write segment ID variable that stores thesegment ID during writing, and a copy start segment ID variable thatstores the segment ID where copy is started with respect to each of thecopy disk devices during copy, during reading the master disk device,

by the storage control device,

(1) storing, when receiving the copy instruction during reading themaster disk device, a value of the read segment ID variable in the copystart segment ID variable of the copy disk device specified by the copyinstruction,

(2) when reading of the master disk device is completed,

-   -   (a) advancing the value of the read segment ID variable to the        next segment ID in order of the circular address,    -   (b) starting writing of the read data into the segments        indicated by the write segment ID variable of all of the copy        disk devices during copy,

(3) when writing of all of the copy disk devices is completed,

-   -   (a) advancing a value of the write segment ID variable to the        next segment ID in order of the circular address,    -   (b) among the copy disk devices during copy, determining those        in which copy of all segments is completed on the basis of the        copy start segment ID variable, and giving notice of completion,        and,    -   (c) when there is the copy disk device during copy, starting        reading from the segment indicated by the read segment ID        variable of the master disk device.

(Supplementary note 9)

A computer readable non-transitory recording medium embodying a program,the program causing a computer to perform a method, the computerconnected to a master disk device that stores data into a plurality ofsegments continuously, and a plurality of copy disk devices that arecopy destinations of the data, the method includes:

receiving a copy instruction for one of the copy disk devices, andrepeating reading and writing of each of the segments in order ofaddress to complete copy, and,

when a first copy disk that is the copy disk device other than a latercopy disk that is the specified copy disk device is during copy whenreceiving the copy instruction, starting copy of the later copy diskfrom the segment during reading, and, after the completion of readingdata of the segment, performing writing into both the first copy diskand the later copy disk.

(Supplementary Note 10)

The method performed by the computer caused by the program embodied inthe computer readable non-transitory recording medium according tosupplementary note 9, the method further includes:

(1) continuing reading and writing of the segments in order of circularaddress such that the segment having the lowest address is targetedafter the segment having the highest address, as long as there is thecopy disk device during copy, and

(2) giving notice of completion for the copy disk device in which copyof all of the segments is completed.

What is claimed is:
 1. A storage control device connected to a masterdisk device that stores data into a plurality of segments continuously,and a plurality of copy disk devices that are copy destinations of thedata, the storage control device comprising: a clone processing unitthat, when receiving a copy instruction for one of the copy diskdevices, repeats reading and writing of each of the segments in order ofaddress to complete copy, and that, when a first copy disk that is thecopy disk device other than a later copy disk that is the specified copydisk device is during copy when receiving the copy instruction, startscopy of the later copy disk from the segment during reading, and, afterthe completion of reading data of the segment, performs writing intoboth the first copy disk and the later copy disk.
 2. The storage controldevice according to claim 1, wherein the clone processing unit (1)continues reading and writing of the segments in order of circularaddress such that the segment having the lowest address is targetedafter the segment having the highest address, as long as there is thecopy disk device during copy, and (2) gives notice of completion for thecopy disk device in which copy of all of the segments is completed. 3.The storage control device according to claim 2, further comprising: astorage region in a management table storing a read segment ID variablethat stores a segment ID that is an identifier of the segment duringreading, a write segment ID variable that stores the segment ID duringwriting, and a copy start segment ID variable that stores the segment IDwhere copy is started with respect to each of the copy disk devicesduring copy, during reading the master disk device, wherein the cloneprocessing unit (1) stores, when receiving the copy instruction duringreading the master disk device, a value of the read segment ID variablein the copy start segment ID variable of the copy disk device specifiedby the copy instruction, (2) when reading of the master disk device iscompleted, (a) advances the value of the read segment ID variable to thenext segment ID in order of the circular address, (b) starts writing ofthe read data into the segments indicated by the write segment IDvariable of all of the copy disk devices during copy, (3) when writingof all of the copy disk devices is completed, (a) advances a value ofthe write segment ID variable to the next segment ID in order of thecircular address, (b) among the copy disk devices during copy,determines those in which copy of all segments is completed on the basisof the copy start segment ID variable, and gives notice of completion,and, (c) when there is the copy disk device during copy, starts readingfrom the segment indicated by the read segment ID variable of the masterdisk device.
 4. The storage control device according to claim 1, whereineach of the segment IDs is a start address of the segments or a sequencenumber.
 5. A storage control method of a storage control deviceconnected to a master disk device that stores data into a plurality ofsegments continuously, and a plurality of copy disk devices that arecopy destinations of the data, the storage control method comprising: bythe storage control device, receiving a copy instruction for one of thecopy disk devices, and repeating reading and writing of each of thesegments in order of address to complete copy; and when a first copydisk that is the copy disk device other than a later copy disk that isthe specified copy disk device is during copy when receiving the copyinstruction, starting copy of the later copy disk from the segmentduring reading, and, after the completion of reading data of thesegment, performing writing into both the first copy disk and the latercopy disk.
 6. The storage control method according to claim 5, furthercomprising: by the storage control device, (1) continuing reading andwriting of the segments in order of circular address such that thesegment having the lowest address is targeted after the segment havingthe highest address, as long as there is the copy disk device duringcopy, and (2) giving notice of completion for the copy disk device inwhich copy of all of the segments is completed.
 7. The storage controlmethod according to claim 6, further comprising: with the use of astorage region in a management table storing a read segment ID variablethat stores a segment ID that is an identifier of the segment duringreading, a write segment ID variable that stores the segment ID duringwriting, and a copy start segment ID variable that stores the segment IDwhere copy is started with respect to each of the copy disk devicesduring copy, during reading the master disk device, by the storagecontrol device, (1) storing, when receiving the copy instruction duringreading the master disk device, a value of the read segment ID variablein the copy start segment ID variable of the copy disk device specifiedby the copy instruction, (2) when reading of the master disk device iscompleted, (a) advancing the value of the read segment ID variable tothe next segment ID in order of the circular address, (b) startingwriting of the read data into the segments indicated by the writesegment ID variable of all of the copy disk devices during copy, (3)when writing of all of the copy disk devices is completed, (a) advancinga value of the write segment ID variable to the next segment ID in orderof the circular address, (b) among the copy disk devices during copy,determining those in which copy of all segments is completed on thebasis of the copy start segment ID variable, and giving notice ofcompletion, and, (c) when there is the copy disk device during copy,starting reading from the segment indicated by the read segment IDvariable of the master disk device.
 8. A computer readablenon-transitory recording medium embodying a program, the program causinga computer to perform a method, the computer connected to a master diskdevice that stores data into a plurality of segments continuously, and aplurality of copy disk devices that are copy destinations of the data,the method comprising: receiving a copy instruction for one of the copydisk devices, and repeating reading and writing of each of the segmentsin order of address to complete copy, and, when a first copy disk thatis the copy disk device other than a later copy disk that is thespecified copy disk device is during copy when receiving the copyinstruction, starting copy of the later copy disk from the segmentduring reading, and, after the completion of reading data of thesegment, performing writing into both the first copy disk and the latercopy disk.
 9. The method performed by the computer caused by the programembodied in the computer readable non-transitory recording mediumaccording to claim 8, the method further comprising: (1) continuingreading and writing of the segments in order of circular address suchthat the segment having the lowest address is targeted after the segmenthaving the highest address, as long as there is the copy disk deviceduring copy, and (2) giving notice of completion for the copy diskdevice in which copy of all of the segments is completed.